The present disclosure relates to a method for disposing blocking material into a component having internal passages, and more particularly to a method for disposing laser blocking material within an interior of an airfoil.
Gas turbine engines typically include a compressor section to pressurize airflow, a combustor section to burn a hydrocarbon fuel in the presence of the pressurized air, and a turbine section to extract energy from the resultant combustion gases. Gas path components, such as turbine blades, often include cooling that may be accomplished by external film cooling, internal air impingement, and forced convection either separately or in combination. In forced convection cooling, compressor bleed air flows through internal chambers to continuously remove thermal energy. The compressor bleed air enters the internal chambers through one or more inlets to the internal chambers, which then discharge though various aperture exits.
Advances in manufacturing have facilitated significantly smaller and more complex internal passages. The cooling air holes are drilled in pre-determined patterns and are contoured to ensure adequate cooling of the airfoil. The cooling air holes duct cooling air from passages on the interior of the airfoil through the hot walls to the exterior. The cooling air provides transpiration cooling as the air passes through the wall and, after the air is discharged from the airfoil, provides film cooling with a film of air on the exterior. The film of cooling air provides a barrier between the airfoil and the hot, working medium gasses.
One process to drill the holes utilizes a laser beam that burns through the wall of the airfoil to form a hole that provides a satisfactory conduit for cooling air. As the laser beam penetrates through the airfoil wall into an interior cavity, the laser beam may strike adjacent structure on the other side of the cavity that may cause unacceptable damage to the airfoil. Accordingly, blocking material may be disposed in the cavity to block the laser beam from striking walls that bound the cavity after the laser beam penetrates through the airfoil wall.
The relatively smaller and more complex passages complicate, if not prevent, the adequate injection of backing materials that fill all internal voids to protect from wall strikes and through wall breakthroughs associated with the laser hole drilling process. One process that attempts to overcome this complication relies solely on the control of filling material temperature and injection pressure, which may not be sufficient for parts with small cavities and complex internal features. Another process relies on controlling injection pressure and part orientation to move entrapped gases within the internal cavities. This process may also not be sufficient for parts with small cavities, complex internal features, nor those that dead-end.